In a known vehicle automatic transmission, a coupled clutch or brake is released when vehicle changes speed, and then is coupled with another clutch or brake in order to provide the next shift range. Shock will occur in this case because of the time lag between the time the clutch or brake is released and the time the clutch or brake is again coupled.
In order to reduce the shock which occurs during a shifting period, engine information, such as the shift up speed, the engine duty, the timing of the clutch or brake coupling and releasing, the coupling speed, etc, are measured, and then fed back and controlled, so that the shock can be reduced. However, the operation of the automatic gear shift will be influenced by the change of movement of the hydraulic switching means (e.g., hydraulic circuit) as the temperature of the working fluid changes. For example, when oil is employed as a working fluid, its viscosity will become high at a low temperature which results in a poor response. For this reason, a time lag occurs between the time the clutch or brake is released, at a releasing side, and the time the clutch or brake is coupled, at coupling side, causing a large shock.